Journal
JOURNAL OF PHYSIOLOGY-LONDON
Volume 593, Issue 2, Pages 385-401Publisher
WILEY-BLACKWELL
DOI: 10.1113/jphysiol.2014.277046
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Funding
- Wellcome Trust [087776]
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An increase in the H2S (hydrogen sulphide, hereafter sulphide) concentration in pulmonary rtery smooth muscle cells (PASMCs) has been proposed to mediate hypoxic pulmonary vasoconstriction (HPV). We evaluated this hypothesis in isolated rat intrapulmonary arteries (IPAs) by examining the effects of the sulphide precursor cysteine and sulphide-synthesis blockers on HPV and also on normoxic pulmonary vasoconstriction (NPV) stimulated by prostaglandin F2(PGF(2)) and by the drug LY83583, which causes contraction in IPAs by increasing cellular reactive oxygen species levels. Experiments with several blockers of cystathionine -lyase (CSE), the enzyme responsible for sulphide synthesis in the vasculature, demonstrated that propargylglycine (PAG, 1mm) had little or no effect on the NPV caused by PGF(2) or LY83583. Conversely, other CSE antagonists tested, aminooxyacetic acid (AOAA, 100m), -cyanoalanine (BCA, 500m) and hydroxylamine (HA, 100m), altered the NPV to PGF(2)(BCA increased, HA inhibited) and/or LY83583 (BCA increased, AOAA and HA inhibited). Preincubating IPAs in physiological saline solution (PSS) containing 1mm cysteine increased the amplitude of the NPV to PGF2 by approximate to 50%, and had a similar effect on HPV elicited by hypoxic challenge with 0% O-2. The enhancement of both responses by cysteine was abolished by pretreatment with 1mm PAG. Measurements carried out with an amperometric electrode demonstrated that incubation with 1mm cysteine under anoxic conditions (to minimize sulphide oxidation) greatly potentiated the release of sulphide from pieces of rat liver and that this release was strongly antagonized by PAG, indicating that at this concentration PAG could enter cells intact and antagonize CSE. PAG at 1mm had no effect on HPV recorded in control PSS, or in PSS supplemented with physiological concentrations of cysteine (10m), cystine (50m) and glutamate (100m) in order to prevent the possible depletion of intracellular cysteine during experiments. Application of a combination of 1mm cysteine and 1mm -ketoglutarate to promote sulphide synthesis via the cysteine aminotransferase/mercaptopyruvate sulphurtransferase (CAT/MST) pathway caused an increase in HPV similar to that observed for cysteine. This was partially blocked by the CAT antagonist aspartate (1mm) and also by PAG. However, HPV was not increased by 1mm -ketoglutarate alone, and HPV in the absence of -ketoglutarate and cysteine was not attenuated by aspartate. Pretreatment of IPAs with dithiothreitol (DTT, 1mm), proposed to promote the conversion of mitochondrial thiosulphate to sulphide, did not increase the release of sulphide from pieces of rat liver in either the presence or the absence of 1mm cysteine, and virtually abolished HPV. The results provide evidence that the sulphide precursor cysteine can promote both NPV and HPV in rat IPA by generating sulphide via a PAG-sensitive pathway, presumably CSE. However, HPV evoked under control conditions was unaffected by the blockade of CSE. Moreover, HPV was not affected by the CAT antagonist aspartate and was blocked rather than enhanced by DTT. The data therefore indicate that sulphide generated by CSE or CAT/MST or from thiosulphate is unlikely to contribute to O-2 sensing during HPV in these arteries.
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